Electrical wave segregation circuit



Au 20, 1940. D. 1.. PLAISTOWE ELECTRICAL WAVE SEGREGATION CIRCUIT Filed April 16, 1937 INVENTOR DONALD L. PLAISTOWE BY 71% ATTORNEY Patented Aug. 20, 1940 UNITED STATE PATENT OFFICE ELECTRICAL WAVE SEGREGATION CIRCUIT Application April 16,

1937, Serial No. 137,171

In Great Britain April 29, 1936 8 Claims.

This invention relates to television and like receivers and more particularly to synchronizing apparatus suitable for use for television and like receivers of the cathode ray tube type.

In modern television and like systems it is usual to secure synchronization as regards scanning action at transmitter and receiver by transmitting, over the same channel with the picture signals, synchronizing signals at the end of each scanning line and at the end of each frame, these synchronizing signals being employed at the receiver to synchronize the blocking oscillators, relaxation oscillation generators or other time base arrangements which provide the necessary scanning deflection at the receiver. The synchronizing signals are of larger amplitude than the maximum picture signals and are usually blacker than black i. e. of larger amplitude thanand of the same sense as picture signals corresponding to black in the subject of transmission. The framing signals are generally of substantially longer duration than the line synchronizing signalseach framing signal may be of duration corresponding to several linesand are sometimes of greater amplitude, although in some systems framing and line synchronizing signals of the same amplitude are employed.

Systems as above described involve the pro visions at the receiver of means for separating the line synchronizing signals and the framing signals and the object of this invention is to provide improved, reliable and sensitive apparatus for separating synchronizing signals from picture signals or for separating line synchronizing signals and framing synchronizing signals from one another.

According to this invention separation of synchronizing signals from picture signals or separation of line synchronizing signals and frame 0 synchronizing signals from one another is obtained in a television or like receiver (adapted to co-operate with a transmitter of the kind transmitting all those-signals over a common channel) by means including a cathode ray tube 45 having a plurality of anodes or targets and means, operated by the signals to be separated or by signals corresponding thereto, are provided for deflecting the ray in said tube in a manner which varies with the different types of signals 50 said anodes being so positioned in said tube that separated signals may be taken from at least one of said anodes.

Where line synchronizing and framing signals which are to be separated by apparatus in 55 accordance with this invention are of different amplitude they may be applied direct to deflecting means in or associated with the tube but where they are of the same amplitude they may be initially separated by means responsive to their different time durations or different frequencies, to produce derived signals which are then applied to the tube.

The invention is illustrated in and further explained in connection with the accompanying drawing, in which Fig. 1 shows one embodiment of my invention,

Fig. 2 is a segregating circuit separating video from synchronizing pulses, and

Fig. 3 is another embodiment of my invention.

Referring to Fig. 1 which shows diagrammatically one arrangement for separating line and framing signals as applied to a receiver for receiving television by a system in which line and framing signals of different amplitudes are transmitted, the mixed synchronizing signals, derived from the output of a radio receiver I are applied through a coupling condenser 2 to an adjustable tapping point 3 upon a resistance 4 one end of which is connected to one (5) of a pair of deflecting plates 5, 6 in a cathode ray tube (the envelope of which is not shown), the other end of said resistance being connected to an adjustable tap 1 upon a potential source whose negative terminal is connected to the earthed cathode 9.of the electron gun of the tube. The other (6) of said pair of plates 5, 6 is connected to another adjustable tap III on said source. The tube, which is preferablya small cheap tube operating with a low voltage (of the order of 250 volts) and a beam current of about 20 micro-amperes has, in addition to the electron gun and the pair of plates already referred to, three anodes ll, I2, I3 arranged side by side. The anode I3 is a plate and the other two anodes ll, I2 which are adjacent one another, are small anodese. g. they may be wires--co-planar withthe plate I3. The anodes are quite close together e. g.-they may be about 1 mm. apart. In front of, i. e. on the gun side of the three anodes. there may be provided a screen electrode M for preventing undesired secondary emission effects. Operating potentials for the three anodes and for the screen may be derived as shown from the source 8 already referred to, the anode l3 being directly connected theretofand each of the other two anodes being connected thereto through its own anode resistance l5 and I6, these anode resistances being of high value. For the case considered-i. e. the case in which the framing signals are of largest amplitudethe anode II (which is furthest from the plate anode I3) is connected through a coupling condenser I! to the grid I8 of a buffer or amplifier valve I9 (which imposes substantially zero load) the anode circuit of this valve feeding separated framing synchronizing pulses into the blocking oscillator or other time base circuit provided for framing action so as to synchronize the action thereof. This oscillator is schematically represented within the rectangle and feeds one pair of deflector plates 2| (the framing plates) of the television reproducer tube which is represented only by its deflector plates. Similarly the anode I2 is capacity coupled through condenser 22 to the grid 23 of another buffer or amplifier valve 24 whose output synchronizes and controls the scanning line time base circuit 25 which feeds the plates 26. The gun of the tube may consist simply of the cathode 3, a negatively biased Whenelt cylinder 21 and an accelerator anode 26. The broken line represents the cathode ray.

The arrangement and adjustments are such that so long as picture signals are applied to the deflecting plate 5 the cathode ray impinges on the plate anode I3 but when a larger amplitude line synchronizing signal is applied the ray is deflected far enough to impinge upon the middle anode I2 and accordingly the line time base 25 will receive a synchronizing pulse. When a still large impulse-a framing impulseis received still greater deflection takes place, the ray impinges on the anode II and the frame time base 26 receives a pulse,

Preferably, in order to facilitate focusslng of the cathode ray, the plate anode I3 is coated with fluorescent material.

In a case where the line and framing signals are of the same amplitude, means responsive to their different frequencies or different durations, may be employed to derive from said signals, signals of different amplitudes and these derived signals may be applied to apparatus as above described with reference to Fig. 1. Alternatively the tube may be provided with separate deflecting plates or other deflecting means for the line and framing signals and these signals after separation by frequency selective or time duration selective apparatus, may be applied to the appropriate deflecting means provided therefor. Thispossibility is indicated schematically in Fig. 1 by showing one additional deflector plate 26. This differs somewhat from an arrangement in which both line and frame signals are impressed on the deflecting plates 5, 6 and makes the deflecting action of each synchronizing signal entirely independent of that of the other. This is especially useful where the synchronizing signals have been passed through differing frequency responsive means.

Apparatus in accordance with this invention will give powerful separated line and framing signals (the cathode ray tube in eflect amplifies these signals apart from the picture signals) with complete separation from one another and from the picture signals. It is moreover sensitive, simple, and relatively cheap for the physical dimensions of the cathode ray tube employed need not be much larger than those of a so-called power wireless receiver valve.

Fig. 2 shows diagrammatically an arrangement for separating line and framing signals, which are blacker than black i. e. which correspond to zero received carrier strength-or at any rate a received carrier strength which is substantially less than the lowest which occurs during picture signal periodsfrom picture signals.

Referring to Fig. 2 there is employed a cathode ray tube having as in Fig. l a cathode 9 and focussing electrode or Wehnelt cylinder 21 and an accelerator anode 28 (together constituting an electron gun), a pair of deflector plates 5, 6, and three plate like anodes II, I2, I3 arranged as shown. Each of the three anodes is connected to a common source (not shown) of anode potential through an anode resistance I5, [6 or 29, and the central anode I2 is earthed through a radio frequency by-pass condenser 36. The anode I I is connected to the plate 5 through a radio frequency choke 3I (providing a D. C. connection only) and the anode I3 is similarly connected to the plate 6 through a choke 32. Received radio or intermediate frequency signals-that is to say modulated carrier energy which has not been rectified by demodulating detention-are applied from receiving apparatus (not shown) in push-pull fashion to the plates 5, 6, through condensers 33, 34. Output is taken off from across resistance I6 through two condensers 35, 36 to two leads 31, 38 one of which leads to the line synchronizing time base circuit (not shown) and the other of which leads to the framing synchronizing time base circuit (not shown). Line and frame synchronizing pulses (both of which appear across the resistance I6) may be separated from one another by means of selecting circuits of any suitable type one of the simplest ways of securing such separation being by suitably dimensioning the condensers and 36.

It will be appreciated that the modulated carrier input fed to the plates 5, 6 will cause the ray 28 to make excursions over the three plates II, I2, I3 swinging back and forth over these plates. At moments of synchronization, i. e. when the carrier strength is zero, the ray will be incident upon the centre plate I2 and accordingly voltage pulses, corresponding to these synchronizing signals will be set up across the resistance I6. In this way the synchronizing signals (line and frame) are separated out from the synchronizing and picture signals.

Fig. 3 shows another embodiment of the invention. Here the two outer anode plates II, I3 are strapped together and connected through a choke 39 to a source (not shown) of anode potential and the central anode I2 is connected to said source through a resistance I6 A lead 38 containing a condenser 36 and choke 4| in series connects the anode I2 with the line frequency time base circuit (not shown), while a lead 31 containing a condenser 35 and a choke 42 in series connects the strapped anodes II, I3 with the framing frequency time base circuit (not shown). Condensers 36 are radio frequency (carrier frequency) by-pass condensers and represents the final intermediate frequency valve of the radio receiver (not otherwise shown) which is presumed to be of the superheterodyne type. If desired the separate strapped anodes II, I3 could be replaced by a single anode with a central aperture.

The operation of Fig. 3 is as follows: The modulated high frequency input applied in pushpull to the plates 5, 6 causes the cathode ray to sweep back and forth across the anodes II, I2, I3 the amplitude of sweep being proportional to the input amplitude. For maximum input amplitudes (corresponding to white in the subject of transmission) the ray sweeps to and fro between the outer edges of anodes II, I3,

while for input amplitudes corresponding to "black in the picture, it sweeps to and fro between the inner edges of the anodes il', l3. The cathode ray is of constant intensity.

Each time the cathode ray falls on an anode H or IS the voltage on these two anodes will drop to a predetermined level and during each cycle of deflection of the cathode ray therefore a high frequency pulse composed of twice the input frequency, will appear on the lead between the two anodes in question. It may be noted that the shape of these pulses is not entirely independent of picture changes from black to white and vice versa. This high frequency pulse component is by-passed by the condenser 30 connected to anodes ll, l3 and the choke 42 in the lead 31 (this choke is not absolutely essential) prevents any high frequency being passed to lead 31. At synchronizing intervals, however, when the high frequency input falls to zero (corresponding to blacker than black) the cathode ray does not reach anodes il', l3 at all but remains on anode l2 and accordingly the voltage on anodes ll, l3 will rise to a predetermined value during such intervals. Since anodes Il', l3 are connected to the anode source through a choke 39 frame synchronizing signals (consisting of positive pulses) will appear on lead 31. Similarly the anode I! will receive a high frequency pulse component of twice the input frequency (this component is by-pas'sed by the appropriate condenser 30 and kept from I lead 38 by choke Al) and a pulse will appear on this anode due to the cathode ray remaining on it during each synchronizingimpulse. Choke 39,

resistance It and condensers 35, 36 are suitably dimensioned to ensure that line frequency pulses appear on one output lead (38) and frame frequency pulses on the other (31).

In both Figs. 2 and 3 the amplitude of swing of the cathode ray.may be adjusted in any conoperate with a transmitter of the kind in which synchronizing signals and. picture signals are transmitted over a common channel, the synchronizing signals lying outside the range of amplitude representative of the picture signals,

a separating circuit arrangement-for separating synchronizing signals from picture signals said arrangement comprising a cathode ray tube having a plurality of anodes and means for applying signals representative of received picture and synchronizing signals to deflecting means provided for deflecting the cathode ray in said tube so that the deflection of said cathode ray depends upon whether a synchronizing signal is being received or whether a picture signal is being received, separated synchronizing signals being taken from at least one of the anode circuits of said cathode ray tube, and means for developing separate controlling potentials from said synchronizing signals.

2. Apparatus as claimed in claim 1 wherein the synchronizing signals lie below the range of amplitudes representative of the picture signals characterized in that carrierenergy, modulated with picture signals and with synchronizing signals, is applied in push-pull to the ray deflecting means the normal (undeflected) position of the ray being such that it is incident upon the central one of three anodes provided in the tube and the deflection being such that said my impinges on all three anodes in succession only for deflecting inputs corresponding to picture signals separated synchronizing signals being taken from the circuit of at least one of said anodes.

3. In a television or. like receiver adapted to 8 cooperate with a transmitter of the kind in which synchronizing signals and picture signals are transmitted over a common channel, the synchronizing signals lying outside the range of amplitude representative of the picture signals, a separating circuit arrangement for separating synchronizingsignals from picture signals said arranging comprising a cathode ray tube having a plurality of anodes and means for applying signals representative of received picture and synchronizing signals to deflecting means provided for deflecting the cathode ray in said tube so that the deflection of said cathode ray depends upon whether a synchronizing signal is being received or whether a picture signal is being received, separated synchronizing signals being taken from a separate anode of said cathode ray tube, a resistance joined to each anode circuit, said resistance being connected together on the sides remote from the anodes, and means for taking developed potentials from across each of the resistance members.

4. The system as claimed in claim 1 wherein three separate anodes are provided in said cathode ray tube, two of said anodes being joined together, a source of anode potential joined to said two anodes, a third anode separately connected to said source of potential, means connected to said anodes for bypassing relatively high frequencies, and frequency selective means between line and frame signals joined in said anode circuits whereby line synchronizing signals may be taken from one portion of the circuit and frame synchronizing signals may be taken from another.

5. In a television or like receiver adapted to 40 cooperate with a transmitter of the kind in which line synchronizing and framing synchronizing signals, which are of diflerent amplitudes are transmitted over a common channel, a separating circuit arrangement for separating the line from 6 the framing synchronizing signals said arrangement comprising a cathode ray tube having a plurality of anodes and means, operated by the line synchronizing and framing synchronizing signals to be separated, for deflecting the ray in said tube by different amounts for the different types of signals, said anodes being so positioned in said tube that, when deflection due to a line signal takes place the ray is incident upon one anode while when deflection due to a. framing 55 signal takes place the ray is incident upon another anode, separated line and framing signals being taken from different anode circuits, and means for developing separate controlling potentials from said synchronizing signals.

6. In a television or like receiver adapted to cooperate with a transmitter of the kind in which linesynchronizing and framing synchronizing signals of differing frequencies are transmitted over a common channel, a separating circuit ar- 05 rangement for separating the line from the framing synchronizing signals said arrangement comprising means for transforming the line and framing signals into signals which are differentiated from onevanother by being of difierent amplitudes, a cathode ray tube having a plurality of anodes, and means operated by the transformed line and framing signals, for deflecting the ray in said tube by different amounts for the different types of signals, said anodes being so positioned in said tube that, when deflection due to a line signal takes place the ray is incident upon one anode while when deflection due to a framing signal takes place the ray is incident upon another anode, separated line and framing signals being taken from different anode circuits, and means for developing separate controlling potentials from said synchronizing signals.

7. In a television or like receiver adapted to cooperate with a transmitter of the kind in which synchronizing signals and picture signals are transmitted over a common channel, the synchronizing signals lying outside the range of amplitude representative of the picture signals, a separating circuit arrangement for separating synchronizing signals from picture signals, said arrangement comprising a cathode ray tube having a plurality of anodes and means for applying signalsrepresentative of received picture and synchonizing signals to deflecting means provided for deflecting the cathode ray in said tube so that the deflection of said cathode ray depends upon whether a synchronizing signal is being received or whether a picture signal is being received, separated synchronizing signals being taken from at least one of the anode circuits of said cathode ray tube, at least one of said anodes being coated with a fiuorescing material whereby focussing of the beam may be indicated.

8. In a television or like receiver adapted to cooperate with a transmitter of the kind in which synchronizing signals and picture signals are transmitted over a common channel, the synchronizing signals lying outside the range of amplitude representative of the picture signals, a separating circuit arrangement for separating synchronizing signals from picture signals, said arrangement comprising a cathode ray tube having a plurality of anodes and means for applying signals representative of received picture and synchronizing signals to deflecting means provided for deflecting the cathode ray in said tube so that the deflection of said cathode ray depends upon whether a synchronizing signal is being received or whether a picture signal is being received, separated synchronizing signals being taken from at least one of the anode circuits of said cathode ray tube, variable biasing means for determining the point of impingement of the cathode ray beam onto one of said anodes.

DONALD LEOPOID PLAISTOWE. 

